The invention relates to a load adjusting device for an actuator that determines the output of an internal combustion engine of a motor vehicle, in particular an actuator designed as a throttle, and is arranged on an actuating shaft, having a reversible actuating drive for moving the actuating shaft between a minimum-load position and a full-load position, having a return spring for biasing the actuating shaft in the minimum-load direction and having an emergency-running spring for biasing the actuating shaft in the full-load direction into an emergency-running position defined by a stop.
A load adjusting device of the above-mentioned type is disclosed by EP 0 378 737 B1 (corresponding to U.S. Pat. No. 5,036,813). The reversible actuating drive of this load adjusting device has an electric motor for moving the actuator. In the event of failure of the actuating drive or of its control system, the actuator is forcibly moved into an emergency-running position by the emergency-running spring and the return spring. This emergency-running position is located between the minimum-load position and the full-load position. In this emergency-running position, the internal combustion engine generates an adequately high torque to move the motor vehicle at a low speed out of a hazardous area. The emergency-running spring and the return spring are in this case each configured as steel springs, the spring force of the emergency-running spring being at least as great as the spring force on the return spring. The drawback with the known load adjusting device is that it is of very complicated construction and is costly to produce. Furthermore, mutually opposed steel springs can set the actuating shaft oscillating and, by this means, make it more difficult to define the emergency-running position exactly.
The invention is based on the problem of configuring a load adjusting device of the type mentioned at the beginning in such a way that it is particularly cost-effective to produce and that the emergency-running position can be defined particularly accurately.
According to the invention, this problem is achieved by the emergency-running spring being produced from an elastic polymer.
As a result of this formation, the emergency-running spring- has inherent damping, so that oscillation of the actuating shaft is reliably prevented. The emergency-running position may therefore be defined simply and is reached reliably in the event of failure of the actuating drive. Furthermore, the emergency-running spring damps shocks on the actuating shaft caused by the stop and therefore leads to low bearing wear of the actuating shaft. Oscillations of the actuator brought about by pressure fluctuations in the intake pipe of the internal combustion engine, and therefore oscillations of the actuating shaft, are likewise damped by the emergency-running spring. As compared with the steel springs of the known load adjusting device, the emergency-running spring can be produced very cost-effectively. This leads to a reduction in the production costs of the load adjusting device according to the invention. The elastic polymer may be, for example, a rubber.
The load adjusting device according to the invention has a particularly compact configuration if the emergency-running spring is arranged between the actuating shaft and a lever that can be moved by the return spring against the stop of the emergency-running position.
The load adjusting device according to the invention can be tuned: particularly simply if the actuating shaft has a direct operative connection to an actuating mechanism of the actuating drive. As a result of this configuration, the ratio of the spring forces is immaterial for the definition of the emergency-running position, since in the position of the lever in which the latter rests against the stop, the emergency-running position is determined only by the emergency-running spring. Between the emergency-running position and the full-load position, the emergency-running spring and the return spring are arranged one behind an other. Therefore, complicated matching of the emergency-running spring with respect to the return spring is not required.
The load adjusting device according to the invention can be designed particularly simply if the lever has a sleeve that surrounds the actuating shaft concentrically.
According to an advantageous development of the invention, the emergency-running spring is configured to guide and hold the sleeve with the stop if the emergency-running spring is shaped like a ring surrounding the actuating shaft. By this means, the load adjusting device according to the invention has particularly few components, which leads to a further reduction in its production costs.
According to another advantageous development of the invention, the spring characteristic of the emergency-running spring can be set simply if the ring-shaped emergency-running spring has recesses. The ratio between the size of the recesses and the mass and the arrangement of the elastic polymer in this case determine the spring characteristic of the emergency-running spring.
The load adjusting device according to the invention can be assembled particularly simply if the emergency-running spring is integrally connected to the sleeve and to a bush that is fixed to the actuating shaft so as to rotate with it. By this means, the emergency-running spring, together with adjacent components, forms a preassembled structural unit. This structural unit may subsequently be mounted simply in its envisaged position on the shaft. At the same time, the emergency-running position of the actuating shaft with the lever resting on the stop can additionally be set simply.
According to another advantageous development of the invention, the emergency-running position can subsequently be set simply if a rotation angle between the bush and the actuating shaft can be set.
A further contribution to reducing the production costs of the load adjusting device according to the invention is made if the lever and the sleeve are produced in one piece from a polymer.
According to another advantageous development of the invention, an envisaged spring force of the emergency-running spring in the emergency-running position can be ensured simply if the sleeve or the bush has a biasing lever for biasing the emergency-running spring and if, when it is in the emergency-running position, the biasing lever is biased against the stop on the respective other component.
According to another advantageous development of the invention, setting the spring force of the emergency-running spring in the emergency-running position can be done particularly simply if the sleeve has a protrusion, the stop being arranged on one side of the protrusion, and a ramp being arranged on the side opposite the stop. Furthermore, as a result of its arrangement on the sleeve, the projection has large dimensions and therefore a high stability.